LOS ANGELES – The first wave of September call-ups began arriving at Dodger Stadium on Monday with catcher Austin Barnes replacing Kiké Hernandez, who went on the DL with a hamstring injury.

Three pitchers will be added Tuesday when rosters can expand. Veteran reliever Joel Peralta will be activated from the DL. Left-hander Ian Thomas and right-hander Mike Bolsinger will be added as well.

There will be more players added as the minor-league season wraps up. But Dodgers president of baseball operations Andrew Friedman doesn’t sound like he has a no cover-charge policy in September. You have to bring something.

“We’re not going to bring guys up just to bring guys up,” Friedman said. “It’s not that I don’t (believe in the value of that). It’s just that when you’re in a pennant race it’s much more about what’s going on in that moment. I think there’s ways to give guys some experience and be around and experience things in a different way. But clubhouses on the road are crowded and it’s just something that we want the guys who are actively participating and helping us win the division.

“With all these guys it’s a conversation and a debate about guys we think really have the potential to be a difference-maker. … If we don’t think guys are quite ready yet, it can be harmful to development.”

The debate over three players not on the 40-man roster will be most interesting – shortstop Corey Seager and left-hander Julio Urias, the Dodgers’ two blue-chip prospects, and right-hander Jharel Cotton who touched four levels of the minor leagues this season while establishing himself as one of the Dodgers’ top pitching prospects.

A year ago, the Dodgers promoted their top prospect from Triple-A, outfielder Joc Pederson, in September as a way to introduce him to the big-league environment. Pederson made three starts and got 28 at-bats in the final month of the 2014 season.

Friedman and his staff will have to do more of a cost-benefit analysis before deciding whether to do the same for Seager who could be their every-day shortstop in 2016. Pederson had to be added to their 40-man roster following last season (in order to protect him from the Rule 5 draft). Seager (and Urias) does not have to be added this winter.

There might not be any more work for Seager this September than there was for Pederson last year. Hernandez’s hamstring injury could open some at-bats at third base to spell Justin Turner – but Seager has made just 19 starts at that position this season.

“I think early it was a little bit of a struggle,” Friedman said of Seager’s part-time transition to third base. “The ball is on you faster than it is at short obviously. But his hands are so good and his work ethic is so good that we knew he would get there, it would just take a little bit of time and I think he’s significantly more comfortable now than he was earlier.”

Friedman acknowledged that it is “definitely” easier for a pitcher to have an impact as a September call-up than a position player. A pitcher like Urias or Cotton can be stashed in the bullpen and used in the most advantageous matchups, almost as a wild card.

“I think anybody that comes up has a chance to catch fire,” Dodgers manager Don Mattingly said. “But most of the time if you’re joining a club that’s winning, you’re not going away from the guys that got you to this point.

“There’s instances where guys get hot and he becomes the guy; we’ve seen it with (Angels) K-Rod (Francisco Rodriguez) a few years back (2002) or guys that have been starters in the minor leagues. They do give you a boost.”

Urias was promoted to the OKC Dodgers on Monday and made his Triple-A debut. He pitched just one inning, allowing three runs on two singles and four walks (all after retiring the first two batters he faced).

Cotton has gone 6-2 with a 2.14 ERA rising from low Class-A to Triple-A since returning from a broken left wrist in late May. Friedman calls the 23-year old right-hander’s changeup “a legitimate major-league out pitch.” Unlike Seager and Urias, the Dodgers will have to add Cotton to the 40-man roster this fall.

MINOR TRADE

The Dodgers completed a minor-league trade before Monday’s deadline for post-season eligibility, acquiring outfielder Justin Ruggiano from the Seattle Mariners in exchange for cash considerations or a player to be named.

Ruggiano, 33, started his pro career with the Dodgers but never played for them. He has a .255 career average in parts of seven seasons with the Tampa Bay Rays, Chicago Cubs, Miami Marlins and Mariners. In Triple-A this season, he has hit .296 with 10 home runs in 49 games.

AROUND THE BASES

Hernandez is the latest Dodgers player sidelined by a hamstring injury. He strained his left hamstring while stretching to beat out a ground ball in the eighth inning of Sunday’s loss to the Chicago Cubs. Given the touchy nature of hamstring injuries, Mattingly said he expects it to “take awhile” before Hernandez is ready to play again. Comparing Hernandez’s injury to the hamstring strains that have sidelined Howie Kendrick and Yasiel Puig, Mattingly said, “Call them all basically about the same.” Kendrick has been on the DL since Aug. 9 and is not ready to start a rehab assignment yet, Mattingly said Monday. Puig was placed on the DL Friday. … Barnes (Riverside Poly High) was named the catcher on the All-PCL team this season. He led the OKC Dodgers with a .315 average and .389 on-base percentage while drawing 35 walks and striking out only 36 times.